I've spent ages looking at sub 7 runs and cannot for the life of me figure out what they are doing to get such good times, i have tried to replicate everything I've seen them do but cant seem to get it

it's a variety of techniques, actually! Here's some very important things to do/keep in mind. (this is pretty damn long, i yap a lot)

1. Room RNG | What rooms you get matters in the run, and you have zero control over it. Unfortunate, but true. I recommend setting times for certain saferooms you'd like to achieve (like splits) and if you dont hit it, reset the run.

2. Slide Techniques | Spam-Sliding and Slide-Jumping are methods you can use to go faster than sprinting. I recommend binding crouch to Q and M1, with M1 being for spamming, and Q being for slide-jumping. Taking advantage of stairs and knowing the best way to slide down them is also very important, which you gain from practice.

3. Knowing when to hide and when to move | in the case of entities, knowing EXACTLY when it's no longer a threat to move is important for minimizing the amount of time you're stopped for. Knowing that you can slide under slugfish's body after the mouth passes, knowing you only die to sorrow when the screenshake ENDS so you can still keep going forward even while your screen is shaking, trailing behind carnation at just the right time, and even only stopping for dozer for less than half a second. If anything, this step is the MOST important, since many many little time saves DEFINITELY add up over the course of the run.

4. Maneuverability | This one's just plain practice. Knowing how to traverse the rooms is majorly important too. Primarily for the run killer rooms (the ones with a bunch of walls in your way with gaps). Knowing the right order to flip levers in lever rooms is also important, since those rooms also take a lot of time.

5. Knowing when to abort | This one's just primarily for saving real life time. If a run is going bad, or you're doing not as good as you think you can/should be doing, there's zero shame in pulling the ol' esc + r + enter for a quick restart. I personally do this for saferoom 0 a lot, if i dont get sub 20.5 for a good start, i reset until I do.

Apply all of these, and you should get a sub 7 in no time!! Again, practice makes perfect. So one thing I'd also recommend is doing a long run to get very used to every entity being in your face, since in the actual run, all of them are only there for a single saferoom section in length.